U.S. patent application number 15/903569 was filed with the patent office on 2018-08-30 for transducer-induced heating and cleaning.
The applicant listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Stephen John Fedigan, David Patrick Magee.
Application Number | 20180246323 15/903569 |
Document ID | / |
Family ID | 63246247 |
Filed Date | 2018-08-30 |
United States Patent
Application |
20180246323 |
Kind Code |
A1 |
Fedigan; Stephen John ; et
al. |
August 30, 2018 |
TRANSDUCER-INDUCED HEATING AND CLEANING
Abstract
In described examples, a transducer vibrates a lens element at a
first frequency and a different second frequency. Controller
circuitry selects one of a cleaning mode and a heating mode in
response to an estimated temperature of the lens element. The
controller circuitry activates the transducer to vibrate the lens
element at the first frequency in response to the controller
circuitry selecting the cleaning mode. The controller circuitry
activates the transducer to vibrate the lens element at the second
frequency in response to the controller circuitry selecting the
heating mode.
Inventors: |
Fedigan; Stephen John;
(Plano, TX) ; Magee; David Patrick; (Allen,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED |
Dallas |
TX |
US |
|
|
Family ID: |
63246247 |
Appl. No.: |
15/903569 |
Filed: |
February 23, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62463224 |
Feb 24, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 27/0006 20130101;
B08B 7/02 20130101; B60S 1/56 20130101; B08B 3/12 20130101 |
International
Class: |
G02B 27/00 20060101
G02B027/00; B60S 1/56 20060101 B60S001/56 |
Claims
1. Apparatus, comprising: a lens element; a transducer to vibrate
the lens element at a first frequency and a different second
frequency; and controller circuitry to: determine an estimated
temperature of the lens element; select one of a cleaning mode and
a heating mode in response to the estimated temperature; activate
the transducer to vibrate the lens element at the first frequency
in response to the controller circuitry selecting the cleaning
mode; and activate the transducer to vibrate the lens element at
the second frequency in response to the controller circuitry
selecting the heating mode.
2. The apparatus of claim 1, wherein the lens element is arranged
to expel foreign material when the transducer vibrates the lens
element at the first frequency.
3. The apparatus of claim 2, wherein the transducer is arranged to
also vibrate the lens element at a different third frequency, the
controller circuitry is arranged to activate the transducer to
vibrate the lens element at the first and third frequencies in
response to the controller circuitry selecting the cleaning mode,
the lens element is arranged to expel a first size range of foreign
material when the transducer vibrates the lens element at the first
frequency, the lens element is arranged to expel a second size
range of foreign material when the transducer vibrates the lens
element at the third frequency, the first size range includes
larger foreign material than the second size range, and the
controller circuitry is arranged to activate the transducer to
vibrate the lens element at the third frequency after vibrating the
lens element at the first frequency.
4. The apparatus of claim 1, wherein the transducer is arranged to
heat the lens element by vibrating the lens element at the second
frequency.
5. The apparatus of claim 4, wherein the controller circuitry is
arranged to activate the transducer to heat the lens element by
vibrating the lens element at the second frequency, before the
transducer vibrates the lens element at the first frequency to
expel foreign material.
6. The apparatus of claim 1, wherein the controller circuitry is
arranged to select the heating mode in response to a comparison of
the estimated temperature to the freezing point of water.
7. The apparatus of claim 1, wherein the transducer is arranged to
dry the lens element by vibrating the lens element at the second
frequency.
8. The apparatus of claim 7, wherein the controller circuitry is
arranged to activate the transducer to dry the lens element by
vibrating the lens element at the second frequency, after the
transducer vibrates the lens element at the first frequency to
expel foreign material.
9. The apparatus of claim 1, wherein the controller circuitry is
arranged to activate the transducer in response to the controller
circuitry determining that the estimated temperature is below a
Curie temperature of a piezoelectric material of the
transducer.
10. The apparatus of claim 1, wherein the controller circuitry is
arranged to measure an impedance of the transducer and/or the lens
element, and to determine the estimated temperature in response to
the measured impedance.
11. The apparatus of claim 10, wherein the controller circuitry is
arranged to measure the impedance in response to an excitation of
the transducer.
12. The apparatus of claim 10, wherein the controller circuitry is
arranged to determine the estimated temperature according to an
equation T=A*Z.sup.2+B*Z+C, wherein Z is the measured impedance
when the transducer is activated, A is a constant, B is a constant,
C is a constant, and T is the estimated temperature.
13. The apparatus of claim 1, wherein the lens element is arranged
to remove moisture from an exterior surface of the lens element
when the transducer vibrates the lens element at the first
frequency, by urging the moisture along a path for moisture
migration.
14. A system, comprising: a vehicle including a vehicle body,
wherein the vehicle body includes an interior space sheltered from
an exterior environment; a camera coupled to the vehicle body,
wherein the camera includes a lens element that is transparent and
is exposed to the exterior environment; apparatus including a
transducer to vibrate the lens element at a first frequency and a
different second frequency; and controller circuitry coupled to the
vehicle, wherein the controller circuitry includes a user interface
to receive a command generated in response to operation of the
vehicle by an operator, wherein the controller circuitry is
arranged to: determine an estimated temperature of the lens
element, select one of a cleaning mode and a heating mode in
response to the estimated temperature, activate the transducer to
vibrate the lens element at the first frequency in response to the
controller circuitry selecting the cleaning mode, and activate the
transducer to vibrate the lens element at the second frequency in
response to the controller circuitry selecting the heating
mode.
15. The system of claim 14, wherein the controller circuitry is
arranged to determine the estimated temperature of the apparatus in
response to the command.
16. The system of claim 14, wherein the transducer is arranged to
also vibrate the lens element at a different third frequency, the
controller circuitry is arranged to activate the transducer to
vibrate the lens element at the first and third frequencies in
response to the controller circuitry selecting the cleaning mode,
the lens element is arranged to expel a first size range of foreign
material when the transducer vibrates the lens element at the first
frequency, the lens element is arranged to expel a second size
range of foreign material when the transducer vibrates the lens
element at the third frequency, the first size range includes
larger foreign material than the second size range, and the
controller circuitry is arranged to activate the transducer to
vibrate the lens element at the third frequency after vibrating the
lens element at the first frequency.
17. The system of claim 14, wherein the controller circuitry is
arranged to activate the transducer to heat the lens element by
vibrating the lens element at the second frequency, before the
transducer vibrates the lens element at the first frequency to
expel foreign material, and wherein the controller circuitry is
arranged to select the heating mode in response to a comparison of
the estimated temperature to the freezing point of water.
18. The system of claim 14, wherein the controller circuitry is
arranged to activate the transducer to dry the lens element by
vibrating the lens element at the second frequency, after the
transducer vibrates the lens element at the first frequency to
expel foreign material.
19. A method, comprising: determining an estimated temperature of a
lens element; selecting one of a cleaning mode and a heating mode
in response to the estimated temperature; activating a transducer
to vibrate the lens element at a first frequency in response to
selecting the cleaning mode; and activating the transducer to
vibrate the lens element at a different second frequency in
response to selecting the heating mode.
20. The method of claim 19, wherein activating the transducer
comprises activating the transducer in response to determining the
estimated temperature is below a safe touch temperature on a
surface of the lens element.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/463,224, filed Feb. 24, 2017, which is
incorporated herein by reference in its entirety.
BACKGROUND
[0002] Electronic optical sensors are widely used for generating
electronic images. Often, such sensors (e.g., "cameras") are
located in places remote to a viewer. The remote locations include
places (e.g., external to vehicles) where contaminants (e.g.
moisture and/or dirt) from the environment can cloud or otherwise
obscure the camera lens, such that degraded images are generated by
a camera having an obscured lens. The degradation of the image
quality can decrease safety or security in many applications.
Various techniques for automatically cleaning the camera lenses
include water sprayers, mechanical wipers, or air jet solutions.
Such approaches are not practical or too costly in a variety of
applications.
SUMMARY
[0003] In described examples, a transducer vibrates a lens element
at a first frequency and a different second frequency. Controller
circuitry selects one of a cleaning mode and a heating mode in
response to an estimated temperature of the lens element. The
controller circuitry activates the transducer to vibrate the lens
element at the first frequency in response to the controller
circuitry selecting the cleaning mode. The controller circuitry
activates the transducer to vibrate the lens element at the second
frequency in response to the controller circuitry selecting the
heating mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a block diagram of an example computing device 100
for controlling a transducer coupled to a lens element.
[0005] FIG. 2 is a cross-section view of an example camera lens
cover system.
[0006] FIG. 3 is a waveform diagram of an impedance response of an
example camera lens cover system over a broad frequency range.
[0007] FIG. 4 is a waveform diagram of an impedance response of an
example camera lens cover system over a reduced frequency
range.
[0008] FIG. 5 is a plot diagram showing a linear relationship
between the impedance response of an example camera lens cover
system and operating temperatures thereof while operating at a
selected operating frequency of 20 kHz.
[0009] FIG. 6 is a flow diagram of an example process for
estimating a temperature of an example camera lens cover system in
response to an impedance measurement of the example camera lens
cover system.
[0010] FIG. 7 is an isometric view of an example camera lens cover
system.
[0011] FIG. 8 is an external view of example foreign contaminant
volumes for an example camera lens cover system.
[0012] FIG. 9 is a block diagram of an example signal generator of
an example camera lens cover system.
[0013] FIG. 10 is a flow diagram illustrating an example method of
foreign contaminant removal from an exposed surface of the example
camera lens cover system.
[0014] FIG. 11 is a top view of an example vehicle including
example camera lens cover systems.
DETAILED DESCRIPTION
[0015] In this description: (a) the term "portion" means an entire
portion or a portion that is less than the entire portion; (b) the
term "housing" means a package or a sealed subassembly/assembly,
which can include control circuitry, a transducer, lenses and an
imaging sensor in a local environment that is sealed from an
outside environment.
[0016] Ultrasonic vibration of lens surfaces (including lens
covers) of camera systems (e.g. automotive systems including rear
view and/or surround view systems) can be more cost effective than
various water sprayer, mechanical wiper, or air jet solutions. As
described herein, piezoelectric transducers (e.g., within a camera
housing) can be monitored in a feedback loop structure without
including a thermocouple in the feedback loop. The piezoelectric
transducer is controlled by estimating a temperature of a
piezoelectric transducer, such that, for example, the buildup of
heat (which can be caused by activating the piezoelectric
transducer) is limited by a comparison to a temperature threshold.
The limiting of the buildup of heat helps prevent the permanent
depolarization of the piezoelectric transducer (e.g., which could
adversely affect the ability of the piezoelectric transducer to
vibrate).
[0017] The apparatus and methods described herein for controlling
and operating a piezoelectric transducer can help ensure that the
temperature of the piezoelectric transducer does not reach more
than one-half a Curie temperature (in degrees Celsius) of the piezo
material of the transducer being controlled. In example
embodiments, the transducer lifetime can be extended by the
avoidance of operating the piezoelectric transducer at potentially
damaging temperatures.
[0018] FIG. 1 is a block diagram of a computing device 100 for
controlling a transducer (in a lens cover system 132) coupled to a
lens element (in the lens cover system 132). For example, the
computing device 100 is, or is incorporated into, or is coupled
(e.g., connected) to an electronic system 129, such as a computer,
electronics control "box" or display, controllers (including
wireless transmitters or receivers), or any type of electronic
system operable to process information.
[0019] In example systems, a computing device 100 includes a
megacell or a system-on-chip (SoC) that includes control logic such
as a central processing unit (CPU) 112, a storage 114 (e.g., random
access memory (RAM)) and a power supply 110. For example, the CPU
112 can be a complex instruction set computer (CISC)-type CPU,
reduced instruction set computer (RISC)-type CPU, microcontroller
unit (MCU), or digital signal processor (DSP). The storage 114
(which can be memory such as on-processor cache, off-processor
cache, RAM, flash memory, or disk storage) stores one or more
software applications 130 (e.g., embedded applications) that, when
executed by the CPU 112, perform any suitable function associated
with the computing device 100. The processor is arranged to execute
code (e.g., firmware instructions and/or software instructions) for
transforming the processor into a special-purpose machine having
the structures--and the capability of performing the
operations--described herein.
[0020] The CPU 112 includes memory and logic circuits that store
information that is frequently accessed from the storage 114. The
computing device 100 can be controlled by a user operating a UI
(user interface) 116, which provides output to and receives input
from the user during the execution the software application 130.
The UI output can include indicators such as the display 118,
indicator lights, a speaker, and vibrations. The UI input can
include sensors for receiving audio and/or light (using, for
example, voice or image recognition), and can include electrical
and/or mechanical devices such as keypads, switches, proximity
detectors, gyros, and accelerometers. For example, the UI can be
responsive to a vehicle operator command to clear an exterior
surface of a backup camera of the vehicle.
[0021] The CPU 112 and the power supply 110 are coupled to I/O
(Input-Output) port 128, which provides an interface that is
configured to receive input from (and/or provide output to)
networked devices 131. The networked devices 131 can include any
device (including test equipment) capable of point-to-point and/or
networked communications with the computing device 100. The
computing device 100 can be coupled to peripherals and/or computing
devices, including tangible, non-transitory media (such as flash
memory) and/or cabled or wireless media. These and other such input
and output devices can be selectively coupled to the computing
device 100 by external devices using wireless or cabled
connections. The storage 114 is accessible, for example, by the
networked devices 131. The CPU 112, storage 114, and power supply
110 are also optionally coupled to an external power source (not
shown), which is configured to receive power from a power source
(such as a battery, solar cell, "live" power cord, inductive field,
fuel cell, capacitor, and energy storage devices).
[0022] The transducer controller 138 includes control and signaling
circuitry components for resonating a transducer of the lens cover
system 132, such that the lens element can be cleaned by expelling
foreign material (e.g., shaken clean of moisture). As described
hereinbelow, the transducer controller 138 includes a temperature
calculator 140 for determining a temperature of the lens cover
system 132, such that, for example, the transducer of the lens
cover system 132 is operated within a safe range of operating
parameters.
[0023] FIG. 2 is a cross-section view of an example camera lens
cover system. The camera lens cover system 200 generally includes a
lens element 220, a seal 230, a housing 240, a transducer 250, and
a camera 260. The camera 260 includes a camera lens 262, a camera
base 264, a photodetector 272, and controller circuitry 274. The
transducer 250 is operable to vibrate at a selected frequency (such
as a factory-selected frequency or an operator-selected frequency)
for motivating the dispersal of the moisture 210 (or other foreign
materials) from the exterior (e.g., upper) surface of the lens
element 220.
[0024] The lens element 220 is a transparent element elastically
captivated in a distal (e.g., upper) portion of the housing 240.
The lens element 220 is arranged to receive light from surrounding
areas and to optically couple the received light to the
photodetector 272 (e.g., via the camera lens 262). The lens element
220 is arranged to protect the camera lens 262 against moisture 210
intrusion, for example. The moisture 210 can be in the form of
frost, water drops, and/or a film of condensation. Foreign
materials (such as the moisture 210 and dirt particles) can block
and/or diffuse light, such that at least some of the received light
is prevented from reaching the camera lens (e.g., compound lens)
262. In an embodiment, the lens element 220 can be a focusing lens
(e.g., for refractively focusing light).
[0025] A seal 230 (such as a rubber seal) is arranged to
elastically captivate the lens element 220 to the housing 240 and
to seal a cavity (e.g., in which the camera lens 262 is arranged)
against intrusion of moisture 210 into the cavity. The intrusion of
moisture 210 and other foreign substances into the cavity can
facilitate condensation inside the lens cover system that can
obstruct the camera's view. Moisture inside the lens cover system
can also damage the controller circuitry 274 electronics and/or the
pixels (e.g., pixel cells) of the photodetector 272. The cavity
extends inwards from the lens element 220 to a proximal (e.g.,
lower) portion of the housing 240.
[0026] The cavity is also formed by the camera base 264, which is
coupled to (or formed as part of) the housing 240. The camera base
264 can include a photodetector 272 and controller circuitry 274.
The photodetector 272 can be a video detector for generating
electronic images (e.g., video streams) in response to the focused
light coupled through the lens element 220 and the camera lens
(which can include lenses). The controller circuitry 274 can
include: (a) a printed circuit board; (b) circuitry of the
transducer controller 138; and (c) and the circuitry of the
temperature calculator 140 for controlling the lens cover system
132 (e.g., where such circuitry and the lens cover system are
arranged in a feedback loop structure). The controller circuitry
274 is coupled to external power, control, and information systems
using wiring and/or optical conduits (such as fibers).
[0027] The transducer 250 is mechanically coupled to the lens
element 220. The transducer 250 can be affixed to the lens element
220 by an intervening adhesive layer (e.g., a high-temperature
resistant epoxy). In operation, the transducer 250 is arranged to
vibrate (e.g., at a selected frequency) the lens element 220 in
response to transducer driver signals. The transducer driver
signals are controllably modulated, such that the transducer 250 is
controllably excited in response to the transducer driver signals.
The transducer driver signals can be amplitude modulated, such that
vibrating lens element 220 can controllably expel moisture 210 and
other such foreign material from the external surface of the lens
element 220 (e.g., external to the cavity).
[0028] A lens cover system 132 can include the transducer 250, the
housing 240, the seal 230, and the lens element 220. As described
hereinbelow, the temperature of the lens cover system can be
estimated in response to (e.g., as a function of) electrical
properties of the lens cover system. The transducer 250 can be
controllably excited in response to the estimated temperature to
efficiently remove obscuring foreign material (including
potentially obscuring foreign material) from the lens element 220
without exceed a threshold temperature limit. (Indeed, the
transducer 250 can be destroyed or degraded when operated for
prolonged periods at excessively elevated temperatures.)
[0029] The impedance response of the lens cover system 132 varies
according to the temperature of the lens cover system 132. As
described herein, the relationship between the estimated
temperature of the lens cover system 132 and the measured
electrical impedance of the lens cover system is substantially
linear within a frequency range. FIG. 3, as described hereinbelow,
shows an impedance response of an example lens cover system over a
frequency range of selected temperatures.
[0030] FIG. 3 is a waveform diagram of an impedance response of an
example lens cover system over a broad frequency range. The
waveform diagram 300 includes a lens cover system impedance
response 310. The lens cover system impedance response 310 shows
the impedance in Ohms over a frequency range between 10 kHz to
around 1 MHz. The example lens cover system can be a lens cover
system such as the system 200 described hereinabove.
[0031] The "zeros" of the impedance response correspond to the
series resonance properties, which correspond to the
electromechanical vibration properties (such as resonance) of a
lens cover system that includes the example transducer. The
electromechanical resonances of the system occur at frequencies in
which relatively larger vibration amplitudes occur for a variable
electrical input amplitude stimulus. For example, electromechanical
resonances occur at frequency ranges 321, 322, and 323. The zeros
are indicated by valleys (such as valley 301) in the curve 310. A
reduced frequency range (e.g., for a "zoomed in" view) of the
impedance response 310 is described hereinbelow with respect to
FIG. 4.
[0032] FIG. 4 is a waveform diagram of an impedance response of an
example lens cover system over a reduced frequency range. The
waveform diagram 400 includes an example lens cover system
impedance response 410. The lens cover system impedance response
410 shows the impedance response of the example lens cover system
over a reduced frequency range (e.g., with respect to the frequency
range shown in FIG. 3).
[0033] The lens cover system impedance response 410 includes
discrete temperature curves for indicating the lens cover system
impedance at a discrete temperature selected from a range of
temperatures. The range of selected discrete temperatures extends
from a temperature of - (minus) 40.degree. C. to a temperature of
60.degree. C., where the temperature represented by each
temperature curve differs from the represented temperature of an
adjacent temperature curve by 20.degree. C. The range of
temperatures encompasses operating temperatures potentially
encountered in operation of the example lens cover system in
various example applications.
[0034] For example, the temperature curve 412 shows the example
lens cover system impedance response in Ohms over a frequency range
of around 20 kHz to 40 kHz at a temperature of -40.degree. C.,
whereas the temperature curve 414 shows the lens cover system
impedance response in Ohms over a frequency range of around 20 kHz
to 40 kHz at a temperature of 60.degree. C. The lens cover system
impedance response 410 includes a valley 401, which indicates a
resonance of the example lens cover system at around 29 kHz for all
illustrated temperature responses.
[0035] At frequencies below 150 kHz (e.g., as shown by the lens
cover system impedance response 310), the gain of an impedance
response generally decreases as the temperature increases, such
that the gain of the lens cover system impedance response 410 is
inversely related to temperature within a selected operating
frequency range (e.g., with exceptions occurring around the
locations of resonant frequencies of the example transducer). The
change in the impedance over temperature is linear (e.g., having a
constant slope and having a change in impedance that is
proportional to a step change in temperature).
[0036] For example, the vertical spacing (e.g., for a given
frequency) between each temperature curve between temperature
curves 412 and 414 of a selected operating frequency is equal
(e.g., substantially equal). The selected operating frequency is
selected from a frequency included in a linear response region,
such as the linear response region extending between, at least, 20
kHz and 25 kHz). The equal spacing of the temperature curves
between temperature curves 412 and 414 is indicative of a linear
relationship between an operating temperature and a measured
impedance at a selected operating frequency.
[0037] The temperature of the example transducer can be determined
in response to a measurement of the impedance of the example
transducer. For example, the example transducer is excited to
vibration (e.g., in response to amplitude-modulated driver signals)
at a frequency of a frequency range in which the change in the
transducer impedance over frequency is linear.
[0038] The dependent variable temperature T as a function of the
impedance variable Z for the example transducer is expressed as the
linear equation:
T=-0.29*Z+392.6 (1)
which has a coefficient of determination R.sup.2 value of
R.sup.2=0.9932 (e.g., which is substantially linear, and wherein
the constant "-0.29" is a slope of the linear equation, and the
constant "392.6" is a y-intercept of the linear equation). The
dependent variable temperature T as a function of the impedance
variable Z for the example transducer can also be expressed as the
parabolic equation:
T=A*Z.sup.2+B*Z+C (2)
where A, B and C are constants. When A=0, Equation (2) is reduced
to the linear form (such as the form of Equation (1)). Accordingly,
the selected operating frequency is selected from within a
frequency region within which the relationship between the
estimated temperature and the measured impedance is determinable as
a quadratic function (e.g., according to the Equation (2)).
[0039] The determined relationship between the estimated
temperature of the lens cover system and the actual (e.g.,
empirically measured) temperature of the example lens cover system
is substantially linear when the coefficient of determination
R.sup.2 value is at least 0.95, for example. As the value of the
coefficient of determination R.sup.2 approaches unity, the
statistical variance between an estimated value using the linear
equation and the actual value is minimized. As the value of
coefficient of determination recedes from unity, errors in the
estimation increase, which can result in any of: (a) decreased
temperature operating range; (b) increased safety margins; and (c)
decreased life of the lens cover system.
[0040] FIG. 5 is a plot diagram showing a linear relationship
between the impedance response of an example lens cover system and
operating temperatures thereof while operating at a selected
operating frequency of 20 kHz. As described herein, the operating
temperature of a lens cover system can be estimated by measuring
the impedance of the lens cover system at a selected operating
frequency, and by converting the impedance measurement to an
estimated temperature (e.g., according to the relationship
described by Equation (1) hereinabove). The conversion of the
impedance measurement to an estimated temperature can be executed
in response to calculating the Equation (1) result, and/or by
indexing a lookup table to retrieve a result according to Equation
(1).
[0041] Plot 500 shows the close statistical correlation between
estimated curve 520 (EST) and a corresponding empirically measured
curve 510 (MEAS). The actual (e.g., simulation value of)
temperature is shown by the empirically measured curve 510. The
estimated temperature (e.g., calculated using Equation (1)) is
shown by the estimated curve 520. The estimated curve 520 can be
estimated in simulations by controlling the temperature (e.g., from
-60.degree. C. to 40.degree. C.) to derive impedance measurements
(e.g., ranging from around 1150 Ohms to 1475 ohms) of the example
lens cover system. The empirically measured curve 510 and the
estimated curve 520 are statistically correlated to a high
degree.
[0042] As shown by the plot 500, the relationship between the
estimated temperature of the lens cover system and the actual
(e.g., empirically measured) temperature of the example lens cover
system is linear (e.g., substantially linear). The maximum error
(e.g., determined in simulations between corresponding points of
the estimated curve 520 and the empirically measured curve 510)
shown by plot 500 is 3.7.degree. C. Accordingly, the lens cover
system temperature can be accurately estimated using a simple
linear equation.
[0043] For example, a temperature error 3.7.degree. C. of a
temperature estimate is sufficiently accurate, such that the
example lens cover system can be safely operated when the
transducer controller maintains the estimated operating temperature
of the example lens cover system below a temperature threshold for
estimated temperatures. As described hereinbelow, the operating
temperature threshold for estimated temperatures can be selected in
response to the error margin of the estimated temperature
measurement and the Curie temperature of the example transducer.
The Curie temperature threshold can be a temperature threshold
beyond which the permanent polarization of piezoelectric materials
of the example transducer is degraded (for example, the Curie
temperature threshold can be half of the Curie temperature).
Accordingly, the temperature threshold is for delineating (e.g., an
upper limit of) an operating temperature range below which the
example transducer can be activated without (e.g., accelerated)
depolarization.
[0044] In an embodiment, the impedance data over a range of
temperatures for a selected operating frequency can be measured at
discrete temperatures and stored as a lookup table in memory (e.g.,
which reduces processing requirements for calculating the equation
otherwise calculated to determine an instant operating
temperature). Simple (e.g., one-dimensional) linear interpolation
can be used to more precisely determine the operating temperature
(e.g., depending on a particular application of the described
techniques, such as measuring a temperature outside a vehicle for
determining a control decision described hereinbelow).
[0045] In an embodiment, impedance data measured over a range of
temperatures and over a range of operating frequencies can be
stored. The impedance data can be measured at discrete temperatures
and discrete operating frequencies and stored as a lookup table in
memory (e.g., such that firmware would not have to be programmed
for controlling specific transducers, each of which can be operated
mutually different frequencies according to a selected transducer
and a selected application). Simple (e.g., two-dimensional) linear
interpolation can be used to more precisely determine the operating
temperature for a selected operating frequency.
[0046] FIG. 6 is a flow diagram of an example process for
estimating a temperature of an example lens cover system in
response to an impedance measurement of the example lens cover
system. The flow 600 can be performed by hardware circuits
exclusive of programming commands. For example, the example process
can be executed by apparatus including analog and/or digital
control circuits (such as registers, adders, multipliers, voltage
generators, and comparators) that are arranged (e.g., pipelined)
according to the process 600, described hereinbelow.
[0047] The flow 600 begins at operation 610, in which an example
transducer is activated (e.g., electrically excited at a selected
frequency by assertion of amplitude-modulated transducer driver
signals). For example, the amplitude-modulated transducer driver
signals are asserted to effect excitation of the example lens cover
system at the selected frequency of 20 kHz (which is a frequency at
which a linear relationship exists between the temperature of the
example lens cover system and the impedance of the lens cover
system). The flow continues to operation 620.
[0048] At operation 620, the impedance (e.g., effective impedance)
of the activated example lens cover system is measured. The
impedance can be measured in response to a voltage drop resulting
from coupling the example transducer to the asserted
amplitude-modulated transducer driver signals, for example. Because
the example lens cover system is excited at 20 kHz, the measured
impedance is derived in response to example transducer excitation
at the selected frequency of 20 kHz. The flow continues to
operation 630.
[0049] At operation 630, the measured impedance is converted to an
estimated temperature. The estimated temperature is determined
according to the linear relationship between the impedance of the
example lens cover system and the operating temperature of the
example lens cover system. For example, the measured impedance can
be converted to the estimated temperature by circuits operating
according to the function of Equation (1), and/or the measured
impedance can be converted to the estimated temperature in response
to indexing a lookup table with values for creating the output of
Equation (1). The lookup table includes addressable values that can
be addressed using the independent variable (e.g., the measured
impedance) as the index, and that are output as results for
providing or determining the value of the dependent variable. For
example, the addressable values are determined (e.g.,
pre-calculated before or after deployment of the system 100)
according to Equation (1). The flow continues to operation 640.
[0050] At operation 640, the temperature is compared against a
temperature threshold. The temperature threshold can be determined
in response to the Curie temperature threshold and a safety margin.
The safety margin can be selected in response to the Curie
temperature threshold, the maximum expected error of the estimated
lens cover system temperature, and a margin for "derating" the lens
cover system for increasing product lifetime (e.g., increasing the
mean-time-between-failure reliability factor) of the example lens
cover system. The flow continues to operation 650.
[0051] At operation 650, the activation state of the transducer is
toggled (e.g., activated when the example transducer is in a
deactivated state, or is deactivated when the example transducer is
in an activated state) in response to the comparison at operation
640. For example, the example transducer is deactivated if the
temperature indicates that the example lens cover system has an
operating temperature that approaches a self-damaging temperature.
The example transducer can be deactivated when the comparison at
operation 640 indicates that the estimated temperature exceeds half
of the Curie temperature (in degrees Celsius) of the example
transducer.
[0052] The process 600 can be invoked each time the example
transducer is activated. The length of a periodic interval (e.g.,
fixed period) of time the example transducer is activated can be
limited (for example) for the purpose of periodically re-invoking
the process 600, which in turn limits the accumulation of heat from
operating the example transducer. The example transducer can be
deactivated in response to the expiration of fixed period of time
during which the example transducer is activated. The length of
time selected for limiting the activated time of the example
transducer can be selected in view of the rate of accumulation of
heat during operation at the selected operating frequency and the
relative sizes of safety margins. Accordingly, the rise of
temperature of the example lens cover system is controllably
limited below levels that are likely to permanently (e.g., without
repair) damage the example transducer (e.g., without incurring the
space, cost, and reliability considerations otherwise encountered
by coupling a thermocouple to the example transducer).
[0053] FIG. 7 is an isometric view of an example camera lens cover
system. The camera lens cover system 700 generally includes a
transducer 710, power wires 720, a lens element 730 and bonding
agent 740. The transducer 710 of the camera lens cover system 700
can be a cylindrical transducer such as transducer 250, described
hereinabove, that is arranged to apply ultrasonic vibrations for
cleaning and/or heating a camera lens cover.
[0054] The transducer 710 is arranged to vibrate a mechanically
coupled lens cover (e.g., the lens element 730) in response to
being driven by an electronic amplifier at frequencies ranging from
around 20 kHz to 2.0 MHz. The transducer 710 can be driven at a
given excitation frequency and a resulting impedance sensed by
coupling signals to and from the transducer via the power wires
720. The resulting impedance can be affected by temperature,
mechanical characteristics, electrical characteristics and the
frequency at which the transducer is driven, for example. A lens
element 730 is secured to a distal surface of the transducer 710 by
a bonding agent 740 (e.g. epoxy) disposed (e.g., as a circular
shape) between the distal surface of the transducer 710 and an
adjacent portion of a surface of the lens element 730. The seal
between the transducer element and the lens element 730 helps
prevent the intrusion of moisture into a sealed cavity (e.g., which
can be formed by a camera base, the transducer 710, the lens
element 730, and the bonding agent 740).
[0055] Environmental moisture (e.g., water drops, water droplets
and/or a film of condensation) can adhere to an exterior surface of
the lens element 730. The moisture can occlude light from being
clearly received by a camera lens in the sealed cavity. The
transducer 710 is operable to vibrate at a selected frequency for
motivating the dispersal of the moisture (or other foreign
materials) from the exterior (e.g., outer) surface of the lens
element 730. When droplets of moisture and/or a film of
condensation remain on the exterior surface of the lens element
730, the remaining moisture can cause saturation of the image
sensor optically coupled to the camera lens when, for example,
incident light encounters the exterior surface of the lens element
730 at an oblique angle.
[0056] The exterior surface of the lens element 730 can be formed
without a "lip" (or can be formed with a lip arranged with channels
extending therethrough), which provides a path for moisture
migration during vibration. Vibration of the sealed lens element
urges moisture along the path for moisture migration, for example,
because the vibration helps overcome surface tension of the
moisture (which otherwise helps the moisture to adhere to itself as
well as to adhere to the outer surface of the lens element 730). As
described hereinbelow with respect to FIG. 8, the transducer 710 is
arranged to (e.g., both) vibrate at the selected frequency and to
generate thermal energy for heating the lens element 730.
[0057] FIG. 8 is an external view of foreign contaminant volumes
for an example camera lens cover system. Water drops "contaminate"
a lens surface (e.g., of lens element 730), such that a view
through the lens surface is blocked or otherwise obscured. In an
example, a camera lens cover system is vertically oriented, such
that the lens element 730 is level, and such that moisture is not
removed by gravity (e.g., for the purpose of illustration) during
the moisture removal stages 810, 820, and 830. In the example, the
multi-stage cleaning diagram 800 includes a large-volume cleaning
stage 810 (e.g., for generally removing drops greater than around
15 .mu.L in volume, such as drop 812), a medium-volume cleaning
stage 820 (e.g., for generally removing drops less than around 15
.mu.L in volume, such as drop 822), and a small-volume cleaning
stage 830 (e.g., for removing residual moisture, such as droplets
832).
[0058] In the large-volume cleaning stage 810, the transducer is
arranged to vibrate in a first mode at a first selected frequency
such that water drops of around 4-10 mm (or greater) diameter are
dispersed (e.g., atomized or otherwise reduced in size) in response
to vibration generated at the first selected frequency. In the
first mode (in stage 810), a large-volume cleaning excitation
signal is applied to the transducer to generate vibration at the
first selected frequency. The first selected frequency can be a
frequency in a frequency range at which electromechanical
resonances occur. The first selected frequency can be characterized
by a relatively high frequency vibration that consumes a relatively
high amount of power. The large-volume cleaning stage 810 can be
followed by the medium-volume cleaning stage 820.
[0059] In the medium-volume cleaning stage 820, the transducer is
arranged to vibrate in a second mode at a second selected
frequency, such that water drops (or droplets) of around 1-4 mm
diameter are dispersed (e.g., atomized or otherwise reduced in
size) in response to the vibration generated at the second selected
frequency. In the second mode (in stage 820), a medium-volume
cleaning excitation signal is applied to the transducer to generate
vibration at the second selected frequency. The second selected
frequency can be a frequency in a frequency range at which
electromechanical resonances occur. The second selected frequency
can be a frequency that is lower than the first selected frequency.
The first selected frequency can be characterized by a relatively
low frequency vibration that consumes a relatively low amount of
power. The medium-volume cleaning stage 810 can be followed by a
small-volume cleaning stage 830.
[0060] In the small-volume cleaning stage 830, the transducer is
arranged to vibrate in a third mode at a third selected frequency,
such that water droplets of around 0-1 mm diameter are evaporated
(e.g., atomized or otherwise dispersed) in response to the heat and
vibration generated at the third selected frequency. In the third
mode (in stage 830), a heating excitation signal is applied to the
transducer to generate vibration at the third selected frequency.
The third selected frequency can be a frequency in a frequency
range at which electromechanical resonances occur. The water
droplets of around 0-1 mm diameter are difficult to remove by
vibrations because, for example, the surface tension of the water
as well as the relatively high van der Waals forces exerted between
the surface of the lens cover and the water.
[0061] The third selected frequency can be a frequency that is
higher than the first selected frequency. The third selected
frequency can be characterized by a relatively high frequency
vibration that consumes a relatively high amount of power. The heat
generated by the transducer is thermally coupled to the lens
element via the bonding agent 740 interposed between the transducer
710 and the lens element 730. The heat transferred to the lens
element 730 helps remove any residual droplets, condensates on the
lens element.
[0062] A control system described hereinbelow with respect to FIG.
9 is arranged to control the amount of heat generated so as to not
overheat the piezoelectric material (which can damage the
transducer actuator) and to avoid exceeding safe touch temperatures
on the surface of the transparent element 730. The transducer
temperature can be estimated by measuring the impedance of the lens
cover system as described hereinabove.
[0063] FIG. 9 is a block diagram of an example signal generator of
an example camera lens cover system. For example, the signal
generator 900 is arranged to control signals for driving a
transducer of the lens cover system, to monitor the transducer
performance and to change aspects of the drive signals in response
to the monitored transducer performance.
[0064] The signal generator 900 includes a voltage (V) boost
circuit 902 that is arranged to receive power (such as 12 volts
direct current input from a vehicle power system) and to generate a
50-volt potential (e.g., surge-protected potential) from the
received 12-volt input power. The 50-volt potential is modulated as
described hereinbelow for driving a transducer of the camera lens
cover system.
[0065] The signal generator 900 also includes an embedded core
(such as a microcontroller unit MCU) 910 for executing instructions
to transform the embedded core into a special-purpose machine for
executing the functions of the camera lens cover system controller
920. For example, the camera lens cover system controller 920
includes control algorithms 922, pulse width modulation (PWM)
signal generation circuit 924, temperature estimation and
regulation circuit 926 and system monitoring and diagnostics
circuit 928. Such functions are described hereinbelow with respect
to FIG. 10.
[0066] The camera lens cover system controller 920 is arranged to
select operating parameters (such as cleaning modes, heating modes,
cleaning stages, frequencies and operating temperatures) for the
camera lens cover system in response to monitoring the camera lens
cover system transducer and to control the PWM switching controller
930 in response to the selected operating parameters. For example,
the camera lens cover system controller 920 is arranged to control
PWM switching times of the PWM switching controller 930. The PWM
switching controller 930 is arranged to signal the PWM PreDriver
940 in response to the switching times received from the PWM
switching controller 930. The PWM PreDriver 940 generates control
signals for toggling (e.g., actuating) the switches of the Class D
driver 950. The Class D Driver 950 is a full-bridge rectifier that
is arranged to generate +/-50 volts (e.g., 100 volts peak-to-peak)
for driving the transducer 960. The sense circuitry 970 generate
current and voltage signals for sensing impedance of the camera
lens cover system and transducer 960, which are monitored (e.g.,
buffered) by the transducer monitor 980. The monitor signals are
coupled via a multiplexer (MUX) 990 to the analog-to-digital
converter (ADC) 990 for sampling. The embedded core 910 is arranged
to receive the sampled current and voltage signals, to compute (via
the camera lens cover system controller 920) new PWM signaling, to
perform temperature estimation and regulation and to perform system
monitoring and diagnostics as described hereinbelow with respect to
FIG. 10.
[0067] FIG. 10 is a flow diagram 1000 illustrating an example
method of foreign contaminant removal from an exposed surface of
the example camera lens cover system described herein. At 1002, the
process begins in the camera lens cover system controller described
hereinabove. At 1010, the camera lens cover system controller waits
a period of time (e.g., waits for the system start signal) before
identifying and/or determining the existence (presence) of
contaminants at 1014. If the wait duration is not expired, the wait
duration is updated at 1012, and the process loops back to
1010.
[0068] At 1014, after the wait period has expired, a frequency
measurement device monitors the resonant frequency the example
camera lens cover system to identify (for example) the amount of
contaminant disposed on the exposed surface. For example, the
amount of a contaminant can be determined in response to a measured
frequency response of the camera lens cover system and comparing
the measured frequency response to a database that includes known
frequency responses for given types and amounts for specific
contaminants. At 1020, the camera lens cover system controller
determines whether a contaminating material exists (is present) on
the camera lens cover, such that at least one operation for
cleaning the camera lens cover is initiated. If "YES," then at
1028, the temperature of the example camera lens cover system is
determined, and types of cleaning and heating are selected in
response to the determined temperature as described hereinbelow. If
"NO," then system checks are performed at 1030.
[0069] If at 1020 the presence of a material is not indicated
("NO"), then at 1030, the process initiates system monitoring and
diagnostics tests (e.g., during which the camera lens cover system
is self-tested). At 1032, a decision is made as to whether to
disable the system. For example, the determination whether to
disable the system can be determined in response to the nature of
faults diagnosed at 1030, a response to a user input and/or a
response to whether the power has been turned off to the system. If
the system is to be disabled ("YES"), then at 1034, the system is
shut down. If the system is not to be disabled ("NO"), the process
loops back to 1010 and waits for a specified duration before the
process starts again.
[0070] As described hereinabove, at 1028, the temperature of the
example camera lens cover system is determined. For example, the
temperature of the example camera lens cover system can be
determined in response to (e.g., as a function of) an operating
frequency of an activated transducer as described hereinabove, or
by a temperature sensing device (such as an externally coupled
thermocouple). The process continues at 1050, for example.
[0071] If at 1050 the determined temperature is below the freezing
point of water (e.g., within a margin of error), then at 1052, the
camera lens cover system controller generates a heating signal for
a specified duration (e.g., time period). For example, in response
to a comparison of the determined temperature to the freezing point
of water, the camera lens cover system controller can generate a
heating excitation signal in a heating mode for warming the camera
lens cover system as described hereinabove by exciting the
transducer at a frequency at which the transducer generates
relatively large amounts of heat, which occurs at frequency
locations where the impedance response is small for a given voltage
input. For example, the heating excitation signal in a heating mode
for warming the camera lens cover system can be generated at a
valley (such as the valley of the frequency range 321, which
includes a relatively low impedance value of a selected frequency
range) of a lens cover system impedance response curve (such as
described hereinabove with respect to FIG. 3 and FIG. 4).
[0072] At 1054, the temperature of the example camera lens cover
system is determined. After the temperature is determined (e.g.,
after initiation of a heating or cleaning mode), the process
continues at 1040, after which the process initiates further
operations (described hereinbelow) to ensure, for example, the
transducer is operated within a safe operating region of
temperatures.
[0073] If at 1056 the type and size of detected contaminating
material indicates the contaminating material is to be reduced in
size, then at 1058, a cleaning signal is generated for cleaning the
example camera lens cover system. For example, the camera lens
cover system controller can select a cleaning mode in response to
the size of detected contaminating material. The cleaning mode can
be selected, such that the cleaning signal can be generated as one
of a large-volume cleaning excitation signal, a medium-volume
cleaning excitation signal and a small-volume cleaning excitation
signal. The large-volume cleaning excitation signal can be
generated at a frequency conducive to resonating larger size drops
of water (for example), whereas the medium-volume cleaning
excitation signal can be generated at a frequency conducive to
resonating medium size drops of water (for example) and the
small-volume cleaning excitation signal can be generated at a
frequency conducive to heating small droplets of water. After the
large-volume or medium-volume cleaning signal is generated and
applied at 1058, the process continues at 1054 where the
temperature of the example camera lens cover system is determined
(e.g., to ensure, the transducer is operated within a safe
operating region of temperatures).
[0074] If at 1060, the size of detected contaminating material
indicates small droplets of water (for example), such that drying
is indicated, then at 1062, a heating signal is generated for
cleaning the example camera lens cover system. For example, the
camera lens cover system controller can generate a heating signal
in a heating mode such that water droplets of around 0-1 mm
diameter are evaporated (e.g., atomized or otherwise dispersed) in
response to the heat and vibration generated in response to the
heating signal (e.g., applied at a frequency different from the
respective frequencies of the applied cleaning signals). After the
heating signal is generated and applied at 1062, the process
continues at 1054 where the temperature of the example camera lens
cover system is determined (e.g., to ensure, the transducer is
operated within a safe operating region of temperatures).
[0075] After the temperature is determined (e.g., again) at 1054,
the process continues at 1040, where a decision is made to
determine whether the temperature of the example camera lens cover
system exceeds a temperature threshold. For example, the
temperature threshold can be half of the transducer Curie
temperature, such that the transducer is controlled to operate
within a safe temperature range. If "YES," the process proceeds to
disable the applied signal (e.g. heating or cleaning signal) at
1042. At 1044, cooling of the transducer and/or exposed surface is
initialized (e.g., by entering a delay period during which the
heating or cleaning signal is disabled, such that additional heat
is not generated). At 1046, the process determines the latest
temperature, and in response at 1048, a decision is made to
determine whether the transducer temperature has finished cooling.
For example, the decision can be made in response to the
information determined at 1046, such that the temperature can be
determined to be below a selected temperature threshold. In an
example, the temperature threshold can be half of the transducer
Curie temperature, such that the transducer is controlled to
operate within a safe temperature range. In another example, the
temperature threshold can be less than the transducer Curie
temperature. If "YES" (e.g., when finished cooling), then at 1048,
the process loops back to 1010. If "NO," then at 1048, the process
loops back to 1046, determines a latest temperature and loops back
to 1048 (e.g., for additional cooling).
[0076] If "NO" at 1040 (e.g., when the transducer temperature does
not exceed the temperature threshold), then at 1016, a decision is
made to determine whether the cleaning process is complete. If
"YES," then the process starts again at 1010. If "NO" at 1016, then
at 1018, the cleaning signal duration is updated and the process
loops back to 1020 for additional testing and potential cleaning
operations.
[0077] FIG. 11 is a top view of an example vehicle including
example camera lens cover systems. The vehicle 1110 includes a
vehicle body that includes an interior space sheltered from an
exterior environment. The vehicle 1110 includes at least one camera
coupled to the vehicle body, where each camera includes a lens
element, where the lens element is transparent and is exposed to
the exterior environment. The vehicle also includes at least one
apparatus that includes a transducer arranged to vibrate the lens
element at a selected operating frequency when operating in an
activated state.
[0078] The vehicle 1110 further includes controller circuitry 1150
coupled to the vehicle, wherein the controller circuitry 1150
includes a user interface arranged to receive commands generated in
response to an operator operating the vehicle 1110 from the
interior space of the vehicle, wherein the controller circuitry
1150 is arranged to measure an impedance of the apparatus while the
transducer is operating at the selected operating frequency,
wherein the controller circuitry 1150 is arranged to determine an
estimated temperature of the apparatus in response to the measured
impedance, wherein the controller circuitry 1150 is arranged to
compare the estimated temperature of the apparatus against a
temperature threshold for delineating an operating temperature
range of the apparatus, and wherein the controller circuitry 1150
is arranged to toggle an activation state of the transducer in
response to comparing the estimated temperature of the apparatus
against the temperature threshold. The controller circuitry 1150
can be arranged to measure an impedance of the apparatus in
response to commands received from the operator operating the
vehicle from the interior space of the vehicle 1110. The controller
circuitry 1150 can also arranged to measure an impedance of the
apparatus in response to the operator starting the vehicle
1110.
[0079] The controller circuitry 1150 includes a display 1160 (which
can also include a touch screen) for displaying a synoptic view
1140 in response to each video signal of a local view 1430 of a
local camera (CAM) 1420.
[0080] Modifications are possible in the described embodiments, and
other embodiments are possible, within the scope of the claims.
* * * * *